CYANOBACTERIA BLOOMS BEHAVIOUR IN LAKE HUME BY CHANGING ITS HYDRODYNAMICS

Managing harmful cyanobacteria in lakes is vital for preserving lake ecosystems and for ensuring good quality water supply from the lake to communities. Lake Hume, a major reservoir of the Murray River system, was identified as a source of cyanobacteria in the downstream river during past mega-blooms. The study aims to assess managed flows from an upstream reservoir on temperature stratification and mixing in the lake to potentially suppress cyanobacteria blooms and thus minimise the risk of cyanobacteria intake from hydropower and irrigation outlets during periods of low dam levels. A one-dimensional vertical hydrodynamic model (Lake1D) was used to simulate 15-year time series data on water temperature and stratification within the lake. The outputs were integrated into a cyanobacteria growth model, driven by water temperature and light. Results indicate that reducing water temperature by 3°C could decrease bloom risk, but it requires an unrealistically high volume of cold-water inflows. High cyanobacteria intake in Lake Hume is a concern when water depths fall below 20m and 10m, for the hydropower and irrigation outlets, respectively. Surface cyanobacteria concentrations obtained from in-situ hyperspectral observations coupled with mixing dynamics enable short-term forecasting of cyanobacteria growth. Varying mixing depth scenarios and initial cell counts underpin the importance of integrating high-resolution water temperature and hyperspectral reflectance data with well-calibrated mixing dynamics for accurate cyanobacteria bloom forecasts.

Primary Presenter: Duy Nguyen, CSIRO (duy.nguyen@csiro.au)

Authors:

Klaus Joehnk, CSIRO  (Klaus.Joehnk@csiro.au)

Tapas Biswas, CSIRO  (Tapas.Biswas@csiro.au)